1. Field of the Invention
This invention relates to a sonar system and a method for detecting with the sonar system. Specifically, the invention relates to a sonar system and a method for detecting for use as a recreational fish finder.
2. Description of the Related Art
A sonar system typically consists of a transmitter, a transducer, a receiver, and a display. The transmitter of the sonar system transmits an electrical impulse. The transducer converts the electrical impulse into a sound wave and sends the sound wave through the water. When the sound wave strikes an object, the sound wave rebounds and returns to the sonar system. The sonar return wave strikes the transducer of the sonar system and the transducer converts the sonar return wave into an electrical signal. The receiver filters, amplifies, and detects the sonar return signal. The receiver converts the sonar return signal into a digital signal after its detection and sends the amplified signal to the display.
The receiver section of a conventional sonar system comprises an analog filter and an analog detector. Such conventional sonar receiver sections can be built using a Philips SA604 “High Performance low power FM IF system.” The Philips SA604 is a monolithic low-power FM intermediate frequency (IF) system that incorporates two limiting IF amplifiers, a quadrature detector, muting, a logarithmic received signal strength indicator, and a voltage regulator. The Philips SA604 is typically used in radios for use as an IF amplifier. The Philips SA604 includes a Received Signal Strength Indicator (RSSI) for outputting a logarithmic representation of the signal strength on the IF input.
A disadvantage of conventional sonar systems is that they are manually tuned during the production and do allow for a later adjustment of the center frequency. As a result, tuning cannot be optimized for use with a specific transducer.
An additional disadvantage of conventional sonar systems is that the bandwidth is fixed. A fixed bandwidth makes it impossible for the sonar system to retrieve an optimal time/frequency response in both shallow and deep water, thus affecting the resolution.
Conventional sonar systems have a dynamic range of approximately 120 dB. An analog-to-digital (A/D) converter with a minimum resolution of 20 bits is required to sample sonar return waves digitally within this dynamic range. The expense of a commercially available A/D converter with 20 bits of resolution is too high for practical use in a recreational fishfinder.
It is an object of the invention to provide a sonar system that performs a digital filtration and a digital detection of a sonar carrier wave.
An additional object of the invention is to provide a sonar system with a high sensitivity and a wide dynamic range.
An additional object of the invention is to provide a sonar system with a programmable frequency.
Another object of the invention is to provide a sonar system with an automatic tuning that can be optimized for use with a specific transducer.
Another object of the invention is to provide a sonar system with a programmable bandwidth.
Another object of the invention is to provide a sonar system with an optimal time/frequency response in both shallow and deep water.
Another object of the invention is to provide a sonar receiver section with commercially available components that are of low cost and are suitable for use in a recreational fishfinder.